The present invention relates to a method and device for measuring the cell gap of a liquid crystal display, a liquid crystal display, and a retardation plate used for measuring the cell gap of a liquid crystal display, which enable accurate measurement of the cell gap.
Heretofore, various display devices using liquid crystal materials, such as active-driven-type TFT (thin film transistor) display, PALC (plasma address liquid crystal) display, and duty-driven-type STN (super twisted nematic) display, are known. Especially, the PALC elements are switching elements utilizing plasma discharge, which are expected to be applied to very large-sized displays. Unlike TFT, the PALC panel does not involve semiconductor processes during manufacture, and therefore, it may be manufactured at low cost. PALC also draws attention for its possibility to be applied to a large-size LCD with low energy consumption.
The above-mentioned liquid crystal displays are characterized for example by their lightweight, thin form, and low energy consumption. These advantages of the liquid crystal display hold the key to the upcoming multimedia society, and studies related to application of the LCD to various office automation devices and audio visual equipment are now under way. The liquid crystal displays often utilize a TN (twisted nematic) display mode where the nematic liquid crystal molecules are twisted for approximately 90 degrees near both electrode substrates, or an STN display mode where the liquid crystal molecules are twisted for over 180 degrees.
Japanese Patent Application Laid-Open No. 10-186330 discloses a liquid crystal display with a wide viewing angle and a good display quality. According to the disclosed LCD, the cell gap size is closely related for example to the display color, the response speed, and the orientation stability, so there is a need of a more accurate method for measuring the cell gap. Even further, the accurate information of the cell gap value is very important for designing and evaluating the LCD.
Heretofore, cell gap measurement devices in the market were used to compute the cell gap by measuring the retardation of the liquid crystal layer. According to the prior art, the gap of an empty cell with no liquid crystal material injected thereto is measured using optical interferometry, and the gap of a liquid crystal-injected cell is measured using a crystal rotation method.
However, it was difficult to obtain a highly accurate cell gap value according to the empty cell gap measurement using optical interferometry, since the liquid crystal cells were equipped with ITO transparent electrodes, an orientation film, a color filter and so on, which caused multiple interference. The separation of the measured value was complex, and the obtained value was not very accurate.
Further, when liquid crystal is filled inside the liquid crystal cell, the refractive index difference between the liquid crystal layer and the substrate is small. Therefore, hardly any interface reflection occurs at the substrate, and no interference fringe appears, which makes it almost impossible to measure the cell gap of a cell filled with liquid crystal material in principle.
On the other hand, according to the crystal rotation method, it is capable of measuring only Np liquid crystal cells where the dielectric anisotropy of the normally-white liquid crystal is positive. It could not be used to measure Nn liquid crystal cells where the dielectric anisotropy of the cells have negative dielectric anisotropy.
When the liquid crystal being sandwiched between two parallel substrates is uniaxially and horizontally oriented to the substrate, the light coming in from the substrate surface is separated into two components by the refractive index anisotropy of the liquid crystal. Therefore, the cell gap of the liquid crystal cell may be measured by the incident angle dependence of the transmission light intensity.
Japanese Patent Application Laid-Open No. 3-115804 discloses a light-weight small-size cell gap measurement device characterized in superposing a lower transparent insulative substrate of the measurement device and an upper transparent insulative substrate of the liquid crystal panel to be measured, so that the rubbing direction of the upper substrate is orthogonal to the rubbing direction of the lower substrate. Further, two polarizing sheets are mounted to both sides of these panels so that the absorption axis orientation of one sheet is orthogonal to the absorption axis orientation of the other sheet.
Further, Japanese Patent Application Laid-Open No. 4-80641 discloses comparing the value of spectrum transmitted through a liquid crystal cell being mounted between two polarizers, with the value of spectrum transmitted therethrough with the angle of the polarizers being varied by 90 degrees. According to the invention, the optical retardation, the cell gap and the liquid crystal birefringence of the liquid crystal cell may be measured.
Japanese Patent Application Laid-Open No. 4-184207 discloses detecting the transmitted light energy while varying the impressed voltage, and obtaining the voltage value where the transmission is minimum, in order to perform an easy and accurate measurement.
Moreover, Japanese Patent Application Laid-Open No. 5-71924 discloses measuring the gap of a liquid crystal cell including Np liquid crystal with positive dielectric anisotropy, while applying thereto either high voltage which is more than 50 times the threshold voltage, or high magnetic field which is more than fifty times stronger than the magnetic field.
Japanese Patent Application Laid-Open No. 9-90371 discloses a method for manufacturing a liquid crystal display. The invention involves pressurizing an empty cell so as to maintain the inner pressure of the empty cell to be equal to the pressure provided to the cell after filling the cell with liquid crystal components, radiating monochromatic beam to the cell, and observing the distribution of the interference fringes. According to the method, the uniformity of the gap inside the empty cell could be inspected.
Further, Japanese Patent Application Laid-Open No. 10-232113 notices that when ultraviolet light or near-ultraviolet light is radiated to an orientation film, the orientation film generates fluorescence. The invention discloses radiating a spot light to an empty cell, and receiving the fluorescence generated at the surf ace of both orientation films by CCD sensor elements, in order to measure the gap of an empty cell.
As explained, many methods for measuring the cell gap of a liquid crystal cell are proposed.
However, according to the conventional methods, including the optical interferometry method using light source generating visible radiation capable of measuring only empty cells, and the crystal rotation method for measuring the incident angle dependence of the transmission rate with retardation generated in the inner-plane orientation parallel to the substrate when polarized light is radiated to the substrate of an Np liquid crystal cell with molecules oriented horizontally when no voltage is impressed, it was impossible, without impressing electric field or magnetic field thereto, to measure the incident angle dependence of the transmitted light energy, in order to obtain the retardation of the liquid crystal cells having the following characters. That is, according to the conventional method, it was impossible to measure the cell gap of a liquid crystal cell equipped with a color filter, having an uneven color filter surface or an uneven substrate surface for liquid crystal driving elements, having molecules oriented perpendicularly when no voltage is impressed, and including an Nn liquid crystal material having negative dielectric anisotropy. In other words, it was impossible to measure the cell gap when the liquid crystal molecules were oriented perpendicularly to the substrate, since the cell will not have any optical retardation (optical path) in the inner plane orientation of the substrate (isotropic).
The present invention aims at solving the above-mentioned problems, by providing a method and device for measuring the cell gap of a liquid crystal display, a liquid crystal display, and a retardation plate for a liquid crystal display. The present invention enables to measure the cell gap of a liquid crystal cell accurately and easily, without having to impress voltage to the liquid crystal cell. Since the components of the liquid crystal cell including the glass plate, the color filter, the transparent electrode, and the orientation film are all optically isotropic, the retardation (dLCxc2x7xcex94n) for only the liquid crystal layer in which liquid crystal molecules exist can be measured, and accordingly, the cell gap may be measured.
The present invention provides a cell gap measurement device for measuring liquid crystal cell gap of a liquid crystal display including a liquid crystal layer having liquid crystal molecules in the liquid crystal region being oriented substantially perpendicularly when no voltage is impressed, and a pair of substrates having the liquid crystal layer sandwiched therebetween; the cell gap measurement device comprising a stage for mounting the liquid crystal cell, a pair of uniaxial retardation plates having retardation in their inner planes being mounted to the outer surfaces of the cell with their slow-phase axis orientations arranged; a light source including a polarizer for radiating to the liquid crystal cell polarized light having an azimuthal orientation at an angle of 44 to 46 degrees to the slow-phase axis orientation of the retardation plates; a photo detector having a photo receptor and an analyze, arranged in cross-Nicol to the polarizer against the polarized light, for detecting transmitted light energy of the polarized light; and a rotation unit for changing the pole-angle-oriented incident angle of the polarized light from the direction perpendicular to the slow-phase axis orientation of the retardation plate.
The present invention provides a cell gap measurement device for a liquid crystal display, wherein the rotation unit rotates the light source and the photo receptor of the photo detector in synchronism, when changing the pole-angle-oriented incident angle of the polarized light.
The present invention provides a cell gap measurement device for a liquid crystal display, wherein the rotation unit changes the pole-angle-oriented incident angle by rotating the stage.
Further, the present invention provides a cell gap measurement device for a liquid crystal display, wherein the light source is either a monochromatic laser light source or a light source equipped with an optical colored filter.
The present invention provides a cell gap measurement device for a liquid crystal display, wherein the light source is equipped with a lamp unit having a Y-luminosity filter. As for the wavelength of the light source, it is preferable to use a monochromatic light generated through a band-pass filter or a monochromatic optical laser.
The present invention further provides a cell gap measurement device for a liquid crystal display, wherein the stage is an X-Y stage equipped with a temperature controller and which enables to measure any point.
Further, the present invention provides a cell gap measurement device for a liquid crystal display, wherein the polarizer may be set to any angle.
The present invention provides a cell gap measurement device for a liquid crystal display, wherein the photo detector comprises a photo diode and a low noise amplifier.
Moreover, the present invention provides a cell gap measurement device for a liquid crystal display, wherein the photo detector comprises a display.
The present invention further provides a method for measuring liquid crystal cell gap of a liquid crystal display including a liquid crystal layer having a liquid crystal material with a refractive index difference xcex94n and liquid crystal molecules in the liquid crystal region being oriented substantially perpendicularly when no voltage is impressed, and a pair of substrates having the liquid crystal layer sandwiched therebetween; the method comprising steps of: mounting, with their slow-phase axis orientations arranged, a pair of uniaxial retardation plates having retardation in their inner planes to both outer surfaces of the liquid crystal cell of the liquid crystal display to be measured; radiating to the liquid crystal cell polarized light, having an azimuthal orientation at an angle of 44 to 46 degrees to the slow-phase axis orientation of the retardation plate, while changing the pole-angle-oriented incident angle of the polarized light from the direction perpendicular to the slow-phase axis orientation of the retardation plate; detecting the transmitted light energy by a photo detector having an analyzer arranged in cross-Nicol to a polarizer of a light source of the polarized light; measuring an optical quenching angle where the detected light energy is either minimum or in a quenching state; obtaining retardation of the liquid crystal cell corresponding to the measured optical quenching angle, based on a calibration curve of the liquid crystal cell retardation and the optical quenching angle corresponding to the gap of the retardation plate; and computing the cell gap based on the obtained liquid crystal cell retardation value and the refractive index difference xcex94n of the liquid crystal material.
The present invention provides a method for measuring cell gap of a liquid crystal display, wherein the calibration curve of the liquid crystal cell retardation and the optical quenching angle corresponding to the gap of the retardation plate is obtained through optical calculation.
The present invention further provides a method for measuring cell gap of a liquid crystal display, wherein the calibration curve of the liquid crystal cell retardation and the optical quenching angle corresponding to the gap of the retardation plate is obtained by measuring the liquid crystal display whose refractive index difference xcex94n and cell gap are known.
The present invention further provides a method for measuring cell gap of a liquid crystal display, wherein the retardation of the mounted uniaxial retardation plate is in the range of 10 nm-50 nm.
Moreover, the present invention provides a liquid crystal display comprising a liquid crystal layer having a liquid crystal material with negative dielectric anisotropy and having liquid crystal molecules in the liquid crystal region being oriented substantially perpendicularly when no voltage is impressed, and a pair of substrates having the liquid crystal layer sandwiched therebetween and equipped with perpendicular orientation films; wherein the liquid crystal display further comprises a pair of uniaxial retardation plates having retardation in their inner planes, the retardation being in the range of 10 nm-50 nm, that is mounted to both outer surfaces of the liquid crystal cell, with the slow-phase axis orientations arranged.
The present invention further provides a retardation plate used in the above method for measuring cell gap of a liquid crystal display, wherein the retardation plate has a retardation in its inner plane, the retardation being in the range of 10 nm-50 nm, and which is uniaxial.
According to another aspect of the present invention, the above-mentioned problems are solved by providing a method and device for measuring the cell gap of a liquid crystal display. The present invention enables to measure the cell gap of a liquid crystal cell accurately, easily and non-destructively in a short time, without having to impress voltage to the liquid crystal cell. Further, the present invention enables to measure the gap of not only empty cells having no liquid crystal material injected thereto, but also cells including a liquid crystal layer to which liquid crystal material is injected. Further, the present invention provides a method and device for measuring the cell gap of any type of liquid crystal display with any liquid crystal material, such as a nematic liquid crystal having either positive or negative dielectric anisotropy, or a ferro electric liquid crystal. Moreover, the elements in the material may be in any state of orientation, including TN, STN, HAN, OCB, and ASM.
In order to solve the above-mentioned problems, the present invention provides a method for measuring cell gap of a liquid crystal display equipped with a pair of substrates with electrodes, that is adhered together to form a cell gap with a predetermined size, and a liquid crystal layer sandwiched between the pair of substrates with electrodes; wherein the cell gap is measured by radiating near-infrared light to a liquid crystal cell, reflectively interfering the near-infrared light by the cell gap, and analyzing the obtained interference waveform to compute the cell gap.
Moreover, the present invention provides a device for measuring cell gap of a liquid crystal display comprising an X-Y stage to which the liquid crystal display including a liquid crystal cell to be measured is set, an FT-NIR spectroscope utilizing near-infrared light as light source, a detector unit for detecting the reflected interference light from the liquid crystal cell, and an analysis computing unit for analyzing the spectrum of the obtained interference fringe and computing the cell gap, based on a peak picking method which measures the interval between a peak and a trough of the spectrum, a Fourier transformation method, or a maximum entropy method (MEM).
Further, the present invention provides a device for measuring cell gap of a liquid crystal display, wherein the liquid crystal cell to be measured is either a liquid crystal cell having liquid crystal material injected to the cell gap, or a liquid crystal cell having no liquid crystal material injected thereto.
Even further, the present invention provides a device for measuring cell gap of a liquid crystal display, wherein the liquid crystal cell to be measured includes a color filter, transparent electrodes, and a perpendicular orientation film or a horizontal orientation film laminated on one glass substrate, and liquid crystal driver elements, picture element electrodes, and an orientation film laminated on another substrate.
The present invention also provides a device for measuring cell gap of a liquid crystal display, wherein the liquid crystal display equipped with the liquid crystal cell to be measured is either a transmission-type liquid crystal display or a reflection-type liquid crystal display utilizing driver elements such as TFT or PALC.
Moreover, the present invention provides a device for measuring cell gap of a liquid crystal display, wherein the liquid crystal cell to be measured comprises liquid crystal molecules having TN, STN, vertical (VA), or hybrid-aligned nematic (HAN) orientation.
The present method and device for measuring cell gap of a liquid crystal display utilizes a Fourier transform-near infrared spectroscope (FT-NIR) using near-infrared light as the light source. The liquid crystal cell gap may be measured by analyzing the waveform (spectrum) of the interference fringe obtained through interference reflection of near-infrared light. A halogen lamp or the like is preferably used as the light source of near-infrared light. The FT-NIR spectroscope utilizes a known interferometer, such as a Michelson interferometer or a Mach-Zehnder interferometer, and further utilizes a Hexe2x80x94Ne laser and the like to calibrate the wavelength of the light source. A preferable example of the detector includes semiconductor crystals such as Ge, InSb, and InGaAs.
One example of a known analysis method for computing the cell gap based on an interference fringe spectrum obtained by measuring LCD is the peak picking method, computing the interval between the peak and the trough of the interference fringe. Other methods include the Fourier transformation (FFT) method, which analyzes the frequency of the peak and the trough of the interference fringe, and the maximum entropy method, which performs curve-fitting of the interference fringe waveform.
The present invention utilizes an analysis computing unit for analyzing and computing the cell gap based on the above analysis methods.
The present invention enables to measure a gap in the range of approximately 10 mmxcfx86 to 50 xcexcxcfx86. Especially in the range of 1 mmxcfx86 to 50 xcexcxcfx86, the present invention may be designed to converge the incident beam by an optical lens, so as to maintain a parallel light, and to further focus the light beam through an aperture. When the beam is not focused during measurement, the measured value shows the average value of the whole measurement region. Especially, when the surface of the color filter or the surface of the liquid crystal driving element substrate of the LCD is uneven, it is preferable to focus the beam to a desired region for measurement.
Moreover, the present invention is preferably equipped with an x-y-z, x-y-z-xcex8 stage or an x-y stage for focusing on any measurement area, an optical microscope system, a CCD camera for capturing the microscope image, and a monitor.
Even further, the present invention is preferably equipped with a device which automatically controls the position and focus of the device to plural measurement areas, so that the present measurement device may be assembled in a manufacturing line as an inspecting device.
The glass, the transparent macromolecules, the transparent electrodes and the liquid crystal material are all transparent within the near-infrared light region, so the interference waveform will not be influenced greatly by absorption of light by the electron, vibration and rotation of each component. This feature of the invention enables to analyze the cell gap highly accurately. Moreover, since the FT-NIR spectroscope is capable of accurately calibrating each wavelength, the loss of light source intensity is very small.
Even further, since the color filter, the transparent electrodes and the orientation film provide little influence to the interference waveform, the present invention enables to measure the cell gap highly accurately.
Moreover, the present invention is capable of measuring liquid crystal displays equipped with any type of liquid crystal drive elements, including the reflection-type and the transmission-type.
The method of measuring cell gap according to the present invention enables to measure the cell gap of the LCD regardless of the liquid crystal orientation, since little effect is provided to the interference waveform by the liquid crystal material.
Even further, the present invention enables to measure the cell gap in a very short time and non-destructively. The present invention enables the cell gap to be inspected within the manufacturing line. The present invention enables to manufacture the cell gap measurement device at low cost. Moreover, by assembling the present cell gap measurement device with a liquid crystal injector or a gap-forming device for liquid crystal layers, cell gap inspection and liquid crystal injection may be performed simultaneously.